It has been recently demonstrated in my laboratory that D-amino acids occur fairly commonly in marine invertebrates. Some of these invertebrate species are used as food by humans and other mammals. It is usually assumed that D-amino acids are inactive biologically. However, in certain marine invertebrate species D- amino acids are accumulated by specific transport systems and metabolized. This suggests that D-amino acids may have some normal physiological role in these species. The function of D- amino is currently under investigation but it appears D-amino acids function in osmoregulation and as nutritional resources. D-amino acids may occur in seafood and also in highly processed food which causes racemization of L-amino acids. They are also produced and released by bacterial flora which normally reside in the intestine. It is quite possible that the tissues of mammals also contain D-amino acids and are capable of transporting and metabolizing them. The objective of this project is to test the hypothesis that D-amino acids are physiologically significant in mammals. This will be done by the following methods: surveying a variety of mammalian species for the presence of D-amino acids in their tissues, measuring the transport properties of rabbit and rat intestine and kidney for D-amino acids, and measuring the capacity of mammalian tissues to metabolize D-amino acids. Preliminary experiments will also be conducted on the toxicity of D-amino acids. To my knowledge this is the first comprehensive attempt to examine the role of D-amino acids in mammalian physiology. The findings of this study will be used to support a future proposal for an in depth study of the role of D-amino acids in mammalian tissues.